6.2 Cause X

Aristotle spent much of his life thinking carefully about ethics. He also defended slavery. He was among the most rigorous moral thinkers in history, and he missed one of the largest moral problems of his own society.

In a 2016 talk, the philosophers Toby Ord and Will MacAskill drew a lesson from this kind of example. They suggested that the most valuable thing a movement like effective altruism could do might not be any of the problems it currently works on. It might be finding a problem nobody yet recognises. They called it Cause X.

That is one reason to treat this course's list as provisional. Problems that didn't make this tour, but that some careful people rank highly, include:

• Climate change: very large, with far more resources going in than for the problems in this course. Some still rank it at the top.
• Nuclear war: the original existential risk, still with us.
• Global mental health: depression and anxiety are among the leading causes of disability worldwide, and treatment is scarce in poor countries.
• Wild animal welfare: most animals live in the wild, and many lives there may involve a great deal of suffering. Almost no one knows what, if anything, can responsibly be done.
• How institutions make decisions: improving the judgement of governments and other large organisations could help with every problem on this list.

80,000 Hours keeps a longer, regularly updated list of problem profiles.